1. Field of the Invention
The present invention relates to a capacitor module that houses a number of electric double-layer capacitor cells. The invention also relates to a capacitor bank made up of an assemblage of such capacitor modules. Furthermore, the invention relates to an electrical energy storehouse that houses stacks of such capacitor banks to store electrical energy.
2. Description of the Related Art
Electrical storage capacitor storehouses are being developed to store electric power at night and to release it during daytime peak load periods. Where electric energy is stored using secondary batteries, the secondary batteries themselves occupy space. In addition, further space is necessary to maintain and service them. For example, in the case of a large-sized, lead-acid battery, a stirring device and a pump are indispensable. In the case of a sodium-sulfur battery, the use of auxiliary equipment, including a heater and its power supply, is vital. A secondary battery itself has a large energy density. However, where secondary batteries are assembled in a battery room, space necessary for such auxiliary equipment makes the amount of storage energy per unit volume (electric energy storage density) in the room much smaller than the energy density of each battery itself.
On the other hand, an electric double-layer capacitor (also known as a pseudocapacitor, supercapacitor, ultracapacitor, or electrochemical capacitor) can be charged quickly. Furthermore, it can store a large amount of energy with a much longer cycle life. These great advantages cannot be achieved by the conventional secondary batteries.
The present inventors have already proposed an electric energy storage system (known as an energy capacitor system (ECS)) using electric double-layer capacitors (e.g., Electrical Engineering in Japan, Vol. 116, No. 3, 1996, Translated from Denki Gakkai Ronbunshi, Vol. 115-B, No. 5, May 1995, pp. 501-510). In an ECS, individual capacitors are connected in series. A parallel monitor acting as a voltage-monitoring control device is connected across each capacitor. Maximum charging is enabled within the withstand voltage of each capacitor. A parallel monitor is connected across each capacitor of a capacitor bank consisting of plural capacitors connected in series. When the charging voltage for the capacitor bank exceeds the set value, the parallel monitor acts to bypass or stop the charging current, thus controlling the state of charge of the capacitors.
In this way, voltage-monitoring control devices are ancillary to the electric energy storage system using electric double-layer capacitors. Therefore, where an electric storage room or storehouse is built using electric double-layer capacitors, the amount of electric energy per unit volume is inevitably much smaller than the energy density of each capacitor itself. In the case of an electric double-layer capacitor, the energy density itself is smaller than those of secondary batteries and, therefore, more careful considerations need to be given.